How this calculator works
A straight panel is a chord of the vertex circle. The chord formula gives the number needed to meet a target vertex diameter, rounded up. The usable flat-to-flat diameter is smaller. A gate of another length creates an irregular polygon and needs a separate layout.
Formula
panel length = D sin(pi/N); N = ceil[pi/asin(panel/D)]; assembled D = panel/sin(pi/N); clear diameter = D cos(pi/N); perimeter = N x panel.
Worked example
Six 3 m panels form a regular hexagon with 6 m vertex diameter, 5.1962 m flat-to-flat diameter and 18 m perimeter.
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Frequently asked questions
Why not just divide circumference by panel length?
That treats panels as curved arcs. Straight panels close as a polygon, which is slightly different.
Are posts and a gate included?
Only equal-length straight sides are counted. Add connection hardware and specify any gate separately.
Does this choose an appropriate horse pen size?
No. Choose space, footing and enclosure details for the intended animals and use.